(1)One door station can support up to four indoor phones. (3)Dual calling, Surveillance, intercom and remote door unlocking are main functions. (4)Color TFT screen display, 7 inch big size can show clear image. (5)LED in the door station provide a clear picture even in night time. (6)30 seconds ring tones are available, 30 seconds active surveillance, 120 seconds intercom (7) melody rings set; (8)Hands set indoor phone; (9)Avoid to unlock by error if no calling. (10)Unique design to unlock the door. (11)Prevent to unlock by taking apart the outdoor unit because the outdoor unit has no unlock line. This system unlock by indoor unit. (12) Power Source: DC 12V (13)Operating temperature: -40C~70C